The present invention relates to a safety switch mounted on, for example, a wall surface around a protective door of an industrial machine or the like and operative to interrupt power supply to the industrial machine or the like when the protective door is opened.
Conventionally, the protective door or the like of the industrial machine is provided with the safety switch for the purpose of eliminating the risk of accident where a worker inadvertently gets caught in the machine and injured. The safety switch is designed to disable the machine when the protective door is not completely closed.
The safety switch of this type is electrically connected to the industrial machine such as robots and includes a switch body and an actuator. The switch body is fixed to the wall surface around the protective door while the actuator is fixed to the protective door. The actuator is fixed to such a position as to be opposed to an actuator inlet port of the switch body and to be inserted in a head case at an upper part of the switch body when the protective door is closed (see, for example, Japanese Examined Patent Publication No. 1999-502669 (Page 9, Page 10, FIG. 3, FIG. 6) and Japanese Unexamined Patent Publication No. 2003-31084 ([0035] to [0038] FIG. 4)).
A built-in switch under the head case (operation portion) of the switch body is switched on by the actuator inserted in the head case, so that the electric power is supplied to the industrial machine and the machine is actuated. When the actuator is extracted from the head case by opening the door, on the other hand, the built-in switch is switched off so that the power supply to the machine is interrupted.
The operation portion is centrally provided with a driving cam for moving a working rod of a switch portion located below the operation portion to thereby switch on and off the switch. The driving cam is rotatably supported with a rotary shaft thereof pivoted on an inside surface of a case member of the operation portion. The working rod is urged by a coil spring toward the operation portion or in a direction of movement to switch off the built-in switch.
In a state where the actuator is not inserted in the operation portion, the working rod is pressed down by the driving cam toward the switch portion and against the urging force of the coil spring. Hence, the built-in switch is set to an open position, disabling the power supply to the industrial machine. On the other hand, when the dedicated actuator is inserted in the operation portion, a connecting peg of the actuator presses the driving cam into rotation. Accordingly, the working rod is moved toward the driving cam by the urging force of the coil spring, switching the built-in switch to a closed position so that the electric power is supplied to the industrial machine.
Some of the above-described safety switches have a structure wherein the operation portion and the switch portion are detachably connected to each other. In the case where the operation portion and switch portion are adapted for detachable connection, a fear exists that an excessive impact on the safety switch may cause detachment of the operation portion from the switch portion. For example, in a state where the actuator is not inserted in the operation portion, or namely the working rod is pressed by the driving cam toward the switch portion and sets the switch of the switch portion to the open position, if the operation portion of the safety switch is detached from the switch portion, the working rod is released from the push toward the switch portion by the driving cam. Hence, the working rod is moved toward the operation portion by the urging force of the coil spring. Thus, the switch of the switch portion is switched on by the working rod moved toward the operation portion so that the electric power is supplied to the industrial machine although the actuator is not inserted in the operation portion. The safety switches of the Japanese Examined Patent Publication No. 1999-502669 (Page 9, Page 10, FIG. 3, FIG. 6) and Japanese Unexamined Patent Publication No. 2003-31084 ([0035] to [0038] FIG. 4) take the following measures as provisions against the occurrence of abnormality where the operation portion and the switch portion are detached from each other, whereby the detection of detachment of the operation portion from the switch portion is provided or malfunction caused by the detachment of the operation portion from the switch portion is obviated.
The safety switch disclosed in Japanese Examined Patent Publication No. 1999-502669 (Page 9, Page 10, FIG. 3, FIG. 6) includes a rotatable feeler member. The feeler member includes an engageable end which is removably engageable with the working rod. If the operation portion is detached from the switch portion, the feeler member is released from locking by the operation portion and is rotated by the urging force of the spring, bringing the engageable end thereof into engagement with the working rod and moving the working rod toward the switch portion. According to this arrangement, even if the operation portion is detached from the switch portion, the feeler member locked by the operation portion is released and rotated by the urging force of the spring, bringing the engageable end thereof into engagement with the working rod for moving the working rod toward the switch portion. Hence, the switch of the switch portion is maintained in the open position, disabling the power supply to the industrial machine or the like.
The safety switch disclosed in Japanese Unexamined Patent Publication No. 2003-31084 ([0035] to [0038] FIG. 4) includes a switch as displacement detection means which is switched off in a case where the operation portion is detached from the switch portion and released from the push toward the switch portion by the driving cam so that the working rod is excessively displaced toward the operation portion by the urging force of a spring. The switch as the displacement detection means is connected to an auxiliary power source and alarm separately provided outside of the safety switch such that the displacement detection means is capable of detecting that this switch is switched off because of the operation portion detached from the switch portion. According to the detection result, the safety switch can annunciate failure warning by switching off a power switch or actuating the alarm.